[Intel-gfx] [PATCH 2/5] drm/i915: Allow asynchronous waits on the i915_active barriers

[Tvrtko Ursulin]

On 06/04/2020 10:12, Chris Wilson wrote:
> Allow the caller to also wait upon the barriers stored in i915_active.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>   drivers/gpu/drm/i915/i915_active.c | 60 ++++++++++++++++++++++++++++++
>   drivers/gpu/drm/i915/i915_active.h |  1 +
>   2 files changed, 61 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_active.c b/drivers/gpu/drm/i915/i915_active.c
> index d5e24be759f7..048ab9edd2c2 100644
> --- a/drivers/gpu/drm/i915/i915_active.c
> +++ b/drivers/gpu/drm/i915/i915_active.c
> @@ -542,6 +542,55 @@ static int __await_active(struct i915_active_fence *active,
>   	return 0;
>   }
>   
> +struct wait_barrier {
> +	struct wait_queue_entry base;
> +	struct i915_active *ref;
> +};
> +
> +static int
> +barrier_wake(wait_queue_entry_t *wq, unsigned int mode, int flags, void *key)
> +{
> +	struct wait_barrier *wb = container_of(wq, typeof(*wb), base);
> +
> +	if (i915_active_is_idle(wb->ref)) { /* shared waitqueue, must check! */

Who shares it?

> +		list_del(&wq->entry);
> +		i915_sw_fence_complete(wq->private);
> +		kfree(wq);
> +	}
> +
> +	return 0;
> +}
> +
> +static int __await_barrier(struct i915_active *ref, struct i915_sw_fence *fence)
> +{
> +	struct wait_barrier *wb;
> +
> +	wb = kmalloc(sizeof(*wb), GFP_KERNEL);
> +	if (unlikely(!wb))
> +		return -ENOMEM;
> +
> +	if (!i915_active_acquire_if_busy(ref)) {
> +		kfree(wb);
> +		return 0;
> +	}
> +
> +	if (!i915_sw_fence_await(fence)) {
> +		kfree(wb);
> +		i915_active_release(ref);
> +		return -EINVAL;
> +	}
> +
> +	wb->base.flags = 0;
> +	wb->base.func = barrier_wake;
> +	wb->base.private = fence;
> +	wb->ref = ref;
> +
> +	add_wait_queue(__var_waitqueue(ref), &wb->base);
> +
> +	i915_active_release(ref);
> +	return 0;
> +}
> +
>   static int await_active(struct i915_active *ref,
>   			unsigned int flags,
>   			int (*fn)(void *arg, struct dma_fence *fence),
> @@ -570,6 +619,16 @@ static int await_active(struct i915_active *ref,
>   			return err;
>   	}
>   
> +	if (flags & I915_ACTIVE_AWAIT_BARRIER) {
> +		err = flush_lazy_signals(ref);
> +		if (err)
> +			return err;
> +
> +		err = __await_barrier(ref, arg);
> +		if (err)
> +			return err;
>

Could have a single set of active_acquire_if_busy/release over the 
previous and this new block. Not sure if that would help with any 
atomicity concerns, or if there are such.

  +	}
> +
>   	return 0;
>   }
>   
> @@ -582,6 +641,7 @@ int i915_request_await_active(struct i915_request *rq,
>   			      struct i915_active *ref,
>   			      unsigned int flags)
>   {
> +	GEM_BUG_ON(flags & I915_ACTIVE_AWAIT_BARRIER);

Why is this an error?

>   	return await_active(ref, flags, rq_await_fence, rq);
>   }
>   
> diff --git a/drivers/gpu/drm/i915/i915_active.h b/drivers/gpu/drm/i915/i915_active.h
> index ffafaa78c494..cf4058150966 100644
> --- a/drivers/gpu/drm/i915/i915_active.h
> +++ b/drivers/gpu/drm/i915/i915_active.h
> @@ -195,6 +195,7 @@ int i915_request_await_active(struct i915_request *rq,
>   			      unsigned int flags);
>   #define I915_ACTIVE_AWAIT_EXCL BIT(0)
>   #define I915_ACTIVE_AWAIT_ACTIVE BIT(1)
> +#define I915_ACTIVE_AWAIT_BARRIER BIT(2)
>   
>   int i915_active_acquire(struct i915_active *ref);
>   bool i915_active_acquire_if_busy(struct i915_active *ref);
> 

Regards,

Tvrtko